Conventionally, a soft material has been a suitable material for a contact lens which can be worn comfortably and an intraocular lens which can be transformed and inserted only by small incision of the eyeball without damaging ocular tissue.
As the above soft material, there are a water-containing material which absorbs water, swells and softens, and a material which does not contain water substantially. Oxygen permeability of the water-containing material depends on water content and does not exceed larger than oxygen permeability of water.
Examples of materials from which a water-containing contact lens with high oxygen permeability can be produced is silicone-containing hydrogel, hereinafter referred to as silicone hydrogel, which is disclosed in Japanese Unexamined Patent Publication No. 179422/1991, Japanese Unexamined Patent Publication No. 196177/1991 and Japanese Unexamined Patent Publication No. 196118/1991. The silicone hydrogel is excellent in oxygen permeability because it has higher oxygen permeability than water.
The above silicone hydrogel contains a hydrophobic component, and therefore wettability of the material surface is inferior, resulting in high sticking property of the surface when the material is molded. Furthermore, when the amount of the silicon-containing monomer is increased to improve oxygen permeability of the material, the obtained material is semi-hard, and thus it is difficult to prepare from the material a contact lens which can be comfortably worn or an intraocular lens which can be inserted only by small incision. It is certain that subjective lens comfort becomes bad when such ocular lens is worn or put in. In addition, there is a defect that deposits such as lipid is increased because of high hydrophobic property. On the other hand, when a hydrophilic component is used in a large amount to improve feeling for wearing of the material, oxygen permeability of the material must depend on water content as a matter of course.
A hydrogel material most suitable for an ocular lens has high wettability and low frictional property in addition to high oxygen permeability and ideal rigidity. Such material is most appropriate because lubricity of a lens is maintained from high wettability and low frictional property, achieving comfortable wearing of the lens on the eye. To improve wettability and lower frictional property of a material, the following methods are suggested.
For instance, U.S. Pat. No. 4,099,859 specification discloses a method of covering surface of a contact lens with a hydrophilic monomer and irradiating the surface with ultraviolet ray to graft-polymerize the hydrophilic monomer on the surface of the contact lens material made of silicone rubber. In addition, U.S. Pat. No. 4,143,949 specification discloses a method of hydrophilic coating on a hydrophobic contact lens by radiation-induced polymerization, while each of U.S. Pat. No. 4,311,573 specification and U.S. Pat. No. 4,589,964 specification discloses a method of imparting hydrophilic property to surface of a hydrophobic polymer by graft-polymerizing a vinyl monomer according to decomposition of generated peroxyl group after ozone treatment. There is another disclosure in Japanese Patent Publication No. 2898664 that a crosslinked siloxane-urethane polymer in the state of an interpenetrating network polymer, generally referred to as IPN, with a hydrophilic vinyl polymer is obtained.
However, all of the above methods have various problems such that the method involves complicated steps, uniform treatment of all lenses and confirmation of the degree of treatment are difficult, and that preparation of raw materials is difficult. A desired hydrogel material most suitable for an ocular lens cannot be easily obtained according to these methods.
In addition to the above, the following various materials are proposed.
For instance, a water-insoluble hydrophilic gel comprising a crosslinked copolymer containing 20 to 90% by weight of water-soluble monomers and water-insoluble monomers such as methyl methacrylate and 10 to 80% by weight of a hydrophobic siloxane macromer is disclosed in Japanese Unexamined Patent Publication No. 22487/1979. A hydrophilic composition having improved flexibility and oxygen permeability after hydration, which is a copolymer of a comonomer comprising 15 to 65% by weight of an amide group-containing monomer, 10 to 75% by weight of an organic silicon compound and 0.1 to 65% by weight of an ester of an alkanol and a (meth)acrylic acid is disclosed in Japanese Unexamined Patent Publication No. 500418/1980. A polysiloxane contact lens obtained by polymerizing, with other monomers, a macromer prepared by mixing an organic siloxane oligomer (I) with a (meth)acrylate monomer (II) in a molar ratio (II)/(I) of 2.0 to 2.6 and reacting the mixture with diisocyanate is disclosed in Japanese Unexamined Patent Publication No. 46311/1992. An ocular lens material comprising a copolymer containing a polysiloxane macromonomer and an alkyl(meth)acrylamide as main components in a weight ratio, the polysiloxane macromonomer/the alkyl(meth)acrylamide, of 5/95 to 90/10 is disclosed in Japanese Unexamined Patent Publication No. 121826/1994.
Being obtained from a component containing silicon, particularly silicone, all of the above gel, composition, contact lens and material have excellent oxygen permeability. However, surface wettability is not particularly good or friction property is not sufficiently low, which means that oxygen permeability, surface wettability and low friction property are not achieved simultaneously.
The present invention has been carried in view of the above prior arts. The object of the present invention is to provide an ocular lens material having excellent surface wettability and low surface frictional property in addition to high oxygen permeability and high mechanical strength.